The present invention relates to an improvement in photoelectric sorting device for color sorting apparatus.
Such a color sorting apparatus has been known as having a grain chute, means for supplying grains of different colors to the upper end of the chute, a grain sorting chamber disposed at the lower side of the chute, and a photoelectric sorting device disposed in the grain sorting chamber, the sorting device including a pair of photoelectric chambers each having a photoelectric detector and disposed to oppose to each other across the flux of flow of grains coming down from the chute, the photoelectric chambers being shielded from the sorting chamber by means of transparent window plates, the photoelectric sorting device further including nozzle means adapted to blow air in accordance with the output signals from the photoelectric detectors thereby to separate and sort the grains of different colors by the jet of air.
In this type of known sorting apparatus, there is a problem that the transparent window plates soon become dim due to contamination or attaching by dust powders released from the grains as the latter are blown by the air. In consequence, the amount of light projected by the light source of each photoelectric detector on the grains is reduced to seriously deteriorate the performance of the color sorting operation. To overcome this problem, a troublesome frequent cleaning of the window plates is necessary. The cleaning work is complicated and troublesome particularly when the sorting apparatus incorporates a multiplicity of nozzles of the same type arranged in a horizontal row. Furthermore, since the cleaning of the window plates necessitates a disassembling of the apparatus, the positional or dimensional precision of the parts such as the grain chute, lenses of the light-receiving elements and so forth is deteriorated in the course of the assembling after the cleaning, resulting in a lowered precision of sorting.